Demand for vehicles with lower fuel consumption is continuing to grow with the global movement toward reduction in carbon dioxide emissions, resulting from increasing recent interest in environmental issues. In order to respond to this demand, there is also need to improve tire performance by reducing rolling resistance.
When developing a rubber composition for use in a tire tread, which contributes to the rolling resistance of a tire, it is generally effective to use the loss tangent (tan δ) at around 60° C. as an indicator in consideration of the fact that the temperature of a tire during normal running reaches approximately 60° C. Specifically, when a rubber composition having a low tan δ at around 60° C. is used in tread rubber, heat buildup in a tire can be inhibited, rolling resistance can be reduced, and, as a result, fuel efficiency of the tire can be improved (PTL 1).
It is also important to ensure braking performance on a wet road surface (hereinafter, referred to simply as “wet braking performance”) in order to enable safer running of a vehicle. Accordingly, there is demand for improving fuel efficiency of a tire while also ensuring wet braking performance of the tire.
In response to this demand, PTL 2 discloses a technique for improving wet braking performance in which tan δ of a rubber composition for a tire tread is set as at least 0.95 at 0° C.